EP1446768A1 - Reduction temporelle du bruit et amplification locale des contrastes - Google Patents

Reduction temporelle du bruit et amplification locale des contrastes

Info

Publication number
EP1446768A1
EP1446768A1 EP01274867A EP01274867A EP1446768A1 EP 1446768 A1 EP1446768 A1 EP 1446768A1 EP 01274867 A EP01274867 A EP 01274867A EP 01274867 A EP01274867 A EP 01274867A EP 1446768 A1 EP1446768 A1 EP 1446768A1
Authority
EP
European Patent Office
Prior art keywords
image
structured
images
local
pass filtering
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP01274867A
Other languages
German (de)
English (en)
Inventor
Markus Simon
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Original Assignee
Siemens AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG filed Critical Siemens AG
Publication of EP1446768A1 publication Critical patent/EP1446768A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/70—Denoising; Smoothing
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/20—Image enhancement or restoration using local operators
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/50—Image enhancement or restoration using two or more images, e.g. averaging or subtraction
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T5/00—Image enhancement or restoration
    • G06T5/73—Deblurring; Sharpening
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/20—Special algorithmic details
    • G06T2207/20172—Image enhancement details
    • G06T2207/20182—Noise reduction or smoothing in the temporal domain; Spatio-temporal filtering
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/20—Special algorithmic details
    • G06T2207/20172—Image enhancement details
    • G06T2207/20192—Edge enhancement; Edge preservation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2207/00—Indexing scheme for image analysis or image enhancement
    • G06T2207/20—Special algorithmic details
    • G06T2207/20212—Image combination
    • G06T2207/20216—Image averaging

Definitions

  • the invention relates to a method for processing images, wherein images scanned by at least one detector device are processed, furthermore a device for carrying out the method and a computer program product.
  • this conventional filtering method does not lead to a suppression or reduction of the noise level; Especially in structurally poor image areas, in which due to relatively uniform or homogeneous gray and color value gradients - as is the case, for example, in monotonous blue sky sections of an image - an existing detector appearance is significantly perceptible and thus impairs the image quality.
  • the object is therefore to create a method of the type mentioned at the beginning and a device which is used to carry out this method, and also a computer program product with which the detector noise is reduced and the image quality is increased in the case of sequences of detected images.
  • the object is achieved in that a resultant image is generated from a sequence of temporally successive individual images by averaging the individual images, that structured image areas are identified in an image during a classifying method step and in a further method step in the identified structured image areas. high-pass filtering is performed on the resulting image.
  • the high-pass filtering in the method according to the invention extends to selected areas of an image, which in a previously performed classifying method step as structured areas were recognized.
  • a time-averaged image is generated from images belonging to a sequence, in which the detector noise is significantly reduced due to the averaging over time.
  • the number of images included in a sequence is defined beforehand.
  • the resolution according to the invention is virtually increased by the high-pass filtering, which is limited to the structured image areas, and thus the image quality is improved.
  • the method according to the invention is thus both in video camera devices with high detector performance as well as in devices which have detectors with low detector performance, such as so-called video handsets.
  • a suitable area of application is, for example, the scanning ("scanning *) of texts with abrupt brightness transitions between text and background.
  • the respectively associated intensities are summed up for the image matrix elements corresponding to the position coordinates in the chronologically successive individual images of a sequence and the sum formed thereby is divided by the number of individual images of the sequence.
  • a temporally averaged intensity is thus assigned to each image matrix element or image pixel from the image matrix of the resulting image.
  • the detector noise is reduced in proportion to the number of images on which the temporal averaging is based, the resulting image quality improvement in unstructured image areas with practically homogeneous gray or color values being most clearly detectable.
  • One embodiment of the method according to the invention can consist of successively calculating local changes in the intensity of image matrix elements arranged adjacent to one another according to location coordinates, in order to identify the structured image areas of an image, and that, when a local change reaching or exceeding a predetermined threshold value parameter, the image matrix elements underlying this change are combined structured image area.
  • the image information on which this change is based in each case is assigned to a structurally poor image area.
  • local gradients are calculated in each case, the calculated local gradients in each case with amount standardization.
  • a second-order high-pass filter is used for high-pass filtering.
  • the high-pass filter is designed as a Laplace operator, the Laplace operator forming a second derivative according to location variables.
  • a further development of the method according to the invention can consist in the strength of the high-pass filtering being controlled as a function of the magnitude-normalized gradient calculated in each case, so that, for example, the strength of the high-pass filtering decreases in the transition zones between structured and homogeneous image areas.
  • a resultant image can be generated from a sequence of chronologically successive individual images by averaging the individual images over time and can be buffered
  • structured image areas can be identified in an image during a classifying method step and high-pass filtering in a further method step in the identified structured image areas of the resulting image is feasible.
  • the device according to the invention has a variety of fields of application.
  • the above-mentioned object is further achieved by a computer program product on which the method according to one of claims 1 to 10 is implemented.
  • the computer program product according to the invention can be designed, for example, as a machine program code and thereby requires a relatively small storage space.
  • a detector device In the case of mobile terminals with a video camera function, images or sequences of images are recorded via a taking lens and imaged on a detector device, the detector device often being designed as a CCD array (charge-coupled device).
  • This detector device is used to convert the optical information received into electrical signals, which are converted into digital data by a processor device with an upstream analog-digital converter.
  • the digital data obtained in this way are shown on a display device connected downstream of the processor device, which can be designed, for example, as a miniature TFT display or LCD display.
  • at devices of this type are either pure video camera devices or mobile end devices which can be designed as mobile telephones with a video camera additional function.
  • detectors or detector arrays are often used, which are inexpensive but have a relatively high noise level and accordingly have a high temporal level Fluctuations in the color and gray values of the images determined thereby show which reduce the image quality.
  • detectors typically have a resolution of 352 x 288 pixels or image matrix elements corresponding to the CIF standard image format (“Common Intermediate File *), with the relatively low resolution resulting in coarse scanning effects, particularly when imaging high-contrast object structures.
  • a resulting image is then generated from this sequence of motion-compensated individual images by averaging over time, the resultant image first being temporarily stored. This temporal averaging in the resulting image results in a reduction of the noise compared to the underlying single or source images.
  • To image matrix elements are selected for each individual image of a sequence, which correspond to position coordinates (x, y) in a coordinate system defining the image matrix of the individual images, and the associated intensity is added up and divided by the number n of individual images belonging to the sequence; the intensity resulting therefrom is thus the time-averaged intensity for the corresponding image matrix element in the image matrix of the temporarily stored resulting image.
  • the intensity of an image matrix element is the respective electric field strength measured at the location of the detector device and includes both gray values and color values.
  • a prerequisite for the use of the method according to the invention is that the detector noise obeys a Gaussian distribution, ie the intensity of the detector noise as a function of time follows a Gaussian bell curve.
  • a classification procedure is carried out, with structured and relatively unstructured areas in the buffered
  • Image can be identified and distinguished from one another.
  • local changes in the intensity of image matrix elements which are arranged adjacent to one another according to location coordinates, are successively calculated within the temporarily stored resultant image;
  • this is achieved in that the gradients, ie the first derivatives based on location variables, are calculated between immediately adjacent image matrix elements or pixels and their respective positive definite amounts are formed.
  • these gradient amounts are standardized in such a way that the maximum of all calculated gradient amounts within the image matrix is searched for and set to 1, so that the gradient amounts standardized in this way move in an interval from 0 to 1.
  • a threshold value parameter is defined in the exemplary embodiment, the value of which lies approximately intermediate in the interval limits between 0 and 1; the gradient amounts calculated for the respective underlying image matrix are compared with this threshold value parameter.
  • the assigned image matrix element is assigned to a structured image area of the image matrix.
  • the assigned image matrix element is assigned to an unstructured image area if the respective gradient amount is smaller than this threshold value parameter.
  • high-pass filtering is carried out in the image areas of the image matrix identified as structured according to the classification procedure.
  • a second-order filter is used as the high-pass filter, a so-called laplace filter having proven to be particularly efficient in the exemplary embodiment.
  • the laplace filter is an operator which, when applied to adjacent image matrix elements in the underlying image matrix, locally forms a second derivative of the respectively assigned intensities according to location variables.
  • the filter parameters of this high-pass filter are adapted to the resolution of the detector device used. As a result, the structured areas of the image, eg building edges, are more visible and the noise is reduced, so that there is virtually a higher resolution compared to the original image.
  • the high-pass filtering can be controlled locally by means of the calculated gradient amounts so that the The maximum amount of high-pass filtering in the center of an image area recognized as structured becomes and decreases in its edge zones, so that edge effects are enhanced and the influence of high-pass filtering in the unstructured or homogeneous image areas disappears.
  • a weighting function derived therefrom can be defined by means of the respectively calculated local gradient amounts, with which the different procedural steps of averaging over time and high-pass filtering can be weighted to one another, depending on the type and scope of the structured or unstructured image areas present in the respective image.
  • the device intended for carrying out the method according to the invention has a taking lens and the detector device, the taking lens being used for imaging objects to be detected on the detector device. Furthermore, as already explained above, the device comprises an analog-digital converter device for converting the electrical image signals provided by the detector device, a processor device downstream of the analog-digital converter device, and a display device.
  • a memory device which is electrically connected to the processor device serves to hold a memory-resident program code with the method steps according to the invention. In normal operation, the processor device accesses this program code and thus automatically carries out the method steps according to the invention, the target images calculated and filtered in each case being shown on the display device.
  • the device according to the invention can be designed as a mobile telephone device with an additional video function.
  • the individual procedural steps which include motion compensation, image classification and high-pass filtering, are interpolated two or four times Source images performed. Instead of the 352 x 288 pixel elements of the detector corresponding to the CIF format, the images processed afterwards have 704 x 576 or 1408 x 1152 pixel elements. Missing gray values in the highly interpolated image are calculated on the basis of gray values of pixel elements of the source image that are adjacent thereto, using bilinear interpolation.
  • the method according to the invention for processing a respective sequence of images can improve the image quality with regard to the edge resolution and noise suppression, the images of a respective sequence each showing the same image detail, but in units of a few pixels or Subpixel positions can be shifted from each other.
  • the method according to the invention carries out a temporal averaging to reduce the detector noise and allows classification of the image to be processed in each case into structured and structurally poor image regions on the basis of the determination of the local gradients, the high-pass filtering being carried out on the image regions recognized as structured limited and thereby the resolution is virtually increased.
  • a field of application is, for example, the recognition of texts with abrupt differences in brightness between text and background.
  • panorama images can be generated, which can be assembled from a sequence of successive images recorded by means of a pivoting movement.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Image Processing (AREA)

Abstract

Procédé de traitement d'images selon lequel des images balayées par au moins un dispositif détecteur sont traitées, et dispositif permettant la mise en oeuvre dudit procédé. Selon la présente invention, une image est produite à partir d'une séquence d'images individuelles successives dans le temps, par moyennage temporel des images individuelles, des zones d'image structurées sont identifiées dans une image lors d'une étape de classification selon ledit procédé et un filtrage par filtre passe-haut est opéré dans les zones structurées identifiées de l'image résultante lors d'une autre étape selon ledit procédé. L'établissement d'une valeur moyenne temporelle permet la réduction du bruit de détecteur et le filtrage par filtre passe-haut subséquent qui est sélectivement limité à des zones d'image précédemment reconnues comme étant structurées augmente virtuellement la résolution, si bien que la qualité d'image s'en trouve globalement améliorée.
EP01274867A 2001-11-19 2001-11-19 Reduction temporelle du bruit et amplification locale des contrastes Withdrawn EP1446768A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/DE2001/004341 WO2003049031A1 (fr) 2001-11-19 2001-11-19 Reduction temporelle du bruit et amplification locale des contrastes

Publications (1)

Publication Number Publication Date
EP1446768A1 true EP1446768A1 (fr) 2004-08-18

Family

ID=5648313

Family Applications (1)

Application Number Title Priority Date Filing Date
EP01274867A Withdrawn EP1446768A1 (fr) 2001-11-19 2001-11-19 Reduction temporelle du bruit et amplification locale des contrastes

Country Status (4)

Country Link
US (1) US20050220354A1 (fr)
EP (1) EP1446768A1 (fr)
JP (1) JP2005512200A (fr)
WO (1) WO2003049031A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
TWI692970B (zh) * 2018-10-22 2020-05-01 瑞昱半導體股份有限公司 影像處理電路及相關的影像處理方法

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Publication number Priority date Publication date Assignee Title
US4334244A (en) * 1980-07-28 1982-06-08 Magnavox Government And Industrial Electronics Company Adaptive image enhancement system
KR910006460B1 (ko) * 1988-03-08 1991-08-26 삼성전자 주식회사 디지탈 영상기기에서 프레임 정지화면의 플리커링 감소장치 및 방식
JPH05328127A (ja) * 1992-05-20 1993-12-10 Nikon Corp 画像処理装置
JP3359390B2 (ja) * 1993-09-27 2002-12-24 株式会社リコー 空間フィルタ装置
JP3706206B2 (ja) * 1996-08-16 2005-10-12 富士写真フイルム株式会社 画像フィルタリング方法および装置
EP0883086B1 (fr) * 1997-06-02 2004-04-07 Seiko Epson Corporation Procédé et dispositif pour l'accentuation des contours
US7043080B1 (en) * 2000-11-21 2006-05-09 Sharp Laboratories Of America, Inc. Methods and systems for text detection in mixed-context documents using local geometric signatures
US6728415B2 (en) * 2001-03-30 2004-04-27 Hewlett-Packard Development Company, L.P. Method and apparatus for image processing using adaptive convolution filters

Non-Patent Citations (1)

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See references of WO03049031A1 *

Also Published As

Publication number Publication date
JP2005512200A (ja) 2005-04-28
US20050220354A1 (en) 2005-10-06
WO2003049031A1 (fr) 2003-06-12

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